1. Field of the Invention
This invention relates to a method and apparatus for handling semiconductor wafers used in the production of integrated circuit structures. More particularly, this invention relates to a method and apparatus for handling semiconductor wafers in a manner which will permit transporting of the wafer from one processing station to another without handling of the wafer, thus reducing formation of loose particulate, and which also permits processing of both the top and bottom surfaces of the wafer equally while mitigating the effects of shadowing.
2. Description of the Related Art
During the processing of semiconductor wafers such as silicon wafers to form integrated circuit structures in and on the wafer, it is necessary to perform a number of processing steps which require transport of the wafer to various apparatuses or chambers within an apparatus. Conventionally this involves the direct physical engagement of the wafer, either manually or by robotic means, to move the wafer between such apparatuses or process stations.
Each such step of physical handling of the wafer can result in the dislodgment of particulates from the wafer surfaces during such handling or other damage to the wafer which can lead to in failure of some of the chips or dies, thus lowering the yield of chips per wafer.
Integrated circuit structures are usually formed on or in one surface of a semiconductor wafer. As a result, wafer handling and transfer methodologies have been developed for processes which involve only one surface of a wafer, conventionally the upper surface.
However, there is a growing amount of interest in processing both surfaces of a semiconductor wafer during the construction of integrated circuit structures, and in particular, the necessity to remove oxide films from the backside of wafers without surface contact either front or back. To remove these oxide films that have been deposited, the wafer face (the front surface) is conventionally pushed upward to some grounding surface, thereby endangering the already processed surface with a contacting and rubbing motion creating particulate.
Since the wafer is conventionally supported during processing by resting the bottom surface of the wafer on a support surface, processing of the bottom surface by conventional means can require turning the wafer over to expose the bottom surface. This not only involves extra process steps, but even further direct handling of the wafer as well, which can further add to the risk of damage to the wafer, e.g., from particulates which may become dislodged from the wafer surfaces during such handling.
Furthermore, while supporting the wafer from the sides during processing rather than the bottom would allow access to the bottom surface of the wafer for processing, it is well known that the placement of any device or material near the wafer during processing can cause severe "shadowing" of the process on the wafer, i.e. the placement of a device or material adjacent the wafer during processing results in incomplete etching, deposition, etc. in those areas of the wafer surface immediately adjacent such device or material.
Dean et al U.S. Pat. No. 4,473,455 describes a wafer holding assembly wherein a number of wafers are loaded onto a plate. Pedestal elements engage the backside surfaces of the wafers. The wafers are held in the plate by clips which are attached to springs mounted on the plate and which engage the ends edges and the edge of the front surfaces of the wafers.
Shaw U.S. Pat. Nos. 4,306,731 and 4,779,877 disclose a wafer support assembly comprising a wafer plate assembly having an aperture larger than the diameter of the wafer. Spring clips comprising spring bands or spring wires carried by the wafer plate assembly have arcuate ends which engage the wafer surfaces adjacent the edges of the wafer.
It would, however, be highly desirable to provide a process and apparatus which would permit transport of a wafer from one process station to another or from one apparatus to another without direct handling of the wafer as well as in a manner which would permit equal processing of both sides of a semiconductor wafer without increasing the risk of shadowing of the wafer on either side of the surface of the wafer during processing.